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Showing content from https://docs.aws.amazon.com/amazondynamodb/latest/APIReference/API_streams_GetShardIterator.html below:

GetShardIterator - Amazon DynamoDB

GetShardIterator

Returns a shard iterator. A shard iterator provides information about how to retrieve the stream records from within a shard. Use the shard iterator in a subsequent GetRecords request to read the stream records from the shard.

Note

A shard iterator expires 15 minutes after it is returned to the requester.

Request Syntax

{
   "SequenceNumber": "string",
   "ShardId": "string",
   "ShardIteratorType": "string",
   "StreamArn": "string"
}

Request Parameters

The request accepts the following data in JSON format.

Note

In the following list, the required parameters are described first.

ShardId

The identifier of the shard. The iterator will be returned for this shard ID.

Type: String

Length Constraints: Minimum length of 28. Maximum length of 65.

Required: Yes

ShardIteratorType

Determines how the shard iterator is used to start reading stream records from the shard:

AT_SEQUENCE_NUMBER - Start reading exactly from the position denoted by a specific sequence number.
AFTER_SEQUENCE_NUMBER - Start reading right after the position denoted by a specific sequence number.
TRIM_HORIZON - Start reading at the last (untrimmed) stream record, which is the oldest record in the shard. In DynamoDB Streams, there is a 24 hour limit on data retention. Stream records whose age exceeds this limit are subject to removal (trimming) from the stream.
LATEST - Start reading just after the most recent stream record in the shard, so that you always read the most recent data in the shard.

Type: String

Valid Values: TRIM_HORIZON | LATEST | AT_SEQUENCE_NUMBER | AFTER_SEQUENCE_NUMBER

Required: Yes

StreamArn

The Amazon Resource Name (ARN) for the stream.

Type: String

Length Constraints: Minimum length of 37. Maximum length of 1024.

Required: Yes

SequenceNumber

The sequence number of a stream record in the shard from which to start reading.

Type: String

Length Constraints: Minimum length of 21. Maximum length of 40.

Required: No

Response Syntax

{
   "ShardIterator": "string"
}

Response Elements

If the action is successful, the service sends back an HTTP 200 response.

The following data is returned in JSON format by the service.

ShardIterator

The position in the shard from which to start reading stream records sequentially. A shard iterator specifies this position using the sequence number of a stream record in a shard.

Type: String

Length Constraints: Minimum length of 1. Maximum length of 2048.

Errors

For information about the errors that are common to all actions, see Common Errors.

InternalServerError

An error occurred on the server side.

HTTP Status Code: 500

ResourceNotFoundException

The operation tried to access a nonexistent table or index. The resource might not be specified correctly, or its status might not be ACTIVE.

HTTP Status Code: 400

TrimmedDataAccessException

The operation attempted to read past the oldest stream record in a shard.

In DynamoDB Streams, there is a 24 hour limit on data retention. Stream records whose age exceeds this limit are subject to removal (trimming) from the stream. You might receive a TrimmedDataAccessException if:

You request a shard iterator with a sequence number older than the trim point (24 hours).
You obtain a shard iterator, but before you use the iterator in a GetRecords request, a stream record in the shard exceeds the 24 hour period and is trimmed. This causes the iterator to access a record that no longer exists.

HTTP Status Code: 400

Examples Retrieve a Shard Iterator For a Stream

The following sample returns a shard iterator for the provided stream ARN and shard ID. The shard iterator will allow access to stream records beginning with the given sequence number.

Sample Request


POST / HTTP/1.1
x-amzn-RequestId: <RequestID>
x-amzn-crc32: <CRC32>
Content-Type: application/x-amz-json-1.0
Content-Length: <PayloadSizeBytes>     
X-Amz-Date: <Date> 
X-Amz-Target: DynamoDBStreams_20120810.GetShardIterator

{
    "StreamArn": "arn:aws:dynamodb:us-west-2:111122223333:table/Forum/stream/2015-05-20T20:51:10.252",
    "ShardId": "00000001414576573621-f55eea83",
    "ShardIteratorType": "TRIM_HORIZON"
}

Sample Response


HTTP/1.1 200 OK
x-amzn-RequestId: <RequestId> 
x-amz-crc32: <Checksum>
Content-Type: application/x-amz-json-1.0
Content-Length: <PayloadSizeBytes>
Date: <Date>
 
{         
    "ShardIterator": "arn:aws:dynamodb:us-west-2:111122223333:table/Forum/stream/2015-05-20T20:51:10.252|1|AAAAAAAAAAEvJp6D+zaQ...  <remaining characters omitted> ..."
}